The present invention relates to the immobilization of chemical agents on membranes for the chemical conversion of a substrate into its reaction products and physical separation immediately thereafter of those reaction products.
Applicant in U.S. Pat. No. 4,716,044 disclosed an improved process for obtaining juice from fruit. A puree of fruit is pumped through an elongated, rigid, porous housing having a food grade ultrafiltration membrane secured along inside surfaces thereof. Juices from the puree filter through the membrane and porous walls of the housing as the retained pulp exits the system in a form suitable for human consumption. The puree is optionally pretreated with enzymes to decrease viscosity by chemically converting the substrate prior to physical separation.
It is well known in the food industry to enzymatically treat the foods being processed. In order to retain the enzymes needed to catalyze the chemical reactions common in food processing and other applications, it has become the norm in the art to immobilize enzymes onto insoluble carriers or matrices.
For example, U.S. Pat. No. 4,033,822 discloses the coupling of enzymes to polymeric ultrafiltration membranes. Enzymes are fixed under pressure to the inner surfaces of pores within the membrane. The diameter of the pores are determined by the size of the enzyme and the size of the substrate to be treated. The pores must be larger than the substrate so that it may pass therethrough for catalysis by the enzyme contained therein. Thus, the membrane of the '822 patent provides merely a means for exposure of the substrate to the enzyme. Immediate physical separation is precluded.
Other means of immobilizing catalysts, including enzymes, onto insoluble carriers have included the chelation of the enzymes onto metal oxides as described in U.S. Pat. Nos. 3,912,593 and 4,016,293. While these enzymes are rendered insoluble for the batch or continuous feed treatment of substrates, once again, immediate physical separation is not provided for.
Further examples of the immobilization of enzymes onto insoluble supports include U.S. Pat. No. 4,511,654 which discloses the two-step process of contacting a feed stock containing a substrate with an enzyme immobilized on a solid support followed by physical separation as by passing the pretreated solution through an ultrafiltration membrane. U.S. Pat. No. 4,430,348 describes a ceramic monolith having an active enzyme immobilized thereon through which is passed fermenting beer for the production of low calorie beer.
The present invention is directed to the immobilization of chemical agents onto membranes which are formed-in-place within the matrix of a rigid, porous housing. While numerous chemical agents which will induce a chemical reaction of a substrate into reaction products are within the scope of the present invention, the present discussion focuses primarily on enzymes which are immobilized on metallic membranes by chelation thereto. Such enzymes serve to induce a chemical reaction of a substrate by catalysis. A substrate in accordance with the present invention is any substance on which the given chemical agent immobilized on the membranes may act to induce in some manner a chemical reaction thereof. Thus, a feed stream containing the substrate passes through the housing wherein the substrate is chemically converted as by catalysis upon contact with an enzyme and is physically separated as the product passes through the membrane and the porous walls of the housing while the retentate passes through an exit end of the housing for separate collection.
The process of the present invention may be arranged as either a one-pass, continuous feed system or a recirculating system with the retentate which passes through the exit end of the housing recirculated back into the feed stream as the permeate is separately collected. When arranged for the immobilization of the chemical agent within the housing, preferably both the retentate and the permeate of the present process recirculate until maximum immobilization is achieved.
The retentate and permeate are physically separated generally by size as the smaller permeate products pass through the ultrafiltration membrane and porous housing and the larger retentate is precluded from filtering through the membrane and therefore continues along the length of the tubular housing. However, as is generally known in the art, ultrafiltration membranes may also act to separate species by charge such that a product, although sufficiently small to pass through the membrane, which has a like charge to that of the membrane, will be repulsed from the membrane and maintained in the retentate. Such a charge separation of the products by the membrane is also within the scope of the present invention.